In the winter or spring. At night. When the water in a unique kind of pond in a distinct kind of forest is at a specific depth. And it is raining.

With such a finicky libido, it might come as no surprise that Rana sevosa — spotted, big eyes, about three inches long and with a mating call that has been compared to a human’s snore — is one of the most endangered amphibians in the world.

The fate of the dusky gopher frog will be the first order of business for the Supreme Court as it opens its new term Monday, one member short and at the center of a national debate over the man nominated to fill that position, Brett Kavanaugh. While that battle rages, the justices will focus on a frog.

The frog, once thought to be extinct, lives in the wild exclusively in Mississippi, in the De Soto National Forest. Its potential new home is more than 50 miles away, across the Pearl River in Louisiana, where the frog once lived but has not been seen since the 1960s.

“It’s nowhere around, and it’s not coming back,” said Edward B. Poitevent II, whose family owns most of what the government calls Unit 1, a 1,544-acre swath of land in St. Tammany Parish. He’s challenging the government’s designation of the land, as is Weyerhaeuser, the timber giant, which owns a bit of the land and has a long-term lease to harvest pine trees on the rest.

“This is not a bird that flies or a fish that swims; it’s not going to fly onto my land or swim onto my land, so what are we talking about here?” asks Poitevent, whose family is the largest landowner in the parish, across Lake Pont­chartrain from New Orleans. “How can this be habitat for something that doesn’t exist on the land?”

The government says to think of Unit 1 as an insurance policy, required by the Endangered Species Act. Once a species has been identified as endangered, the government is required to identify critical habitat for the creatures, and the law specifically envisions land that is occupied by the species, and not.

Unoccupied land may be deemed critical only when the government determines it is “essential for the conservation of the species.” The act defines “conservation” to include not just survival, but restoration of the population, and the frog used to live in Alabama, Mississippi and Louisiana.

A panel of experts said Unit 1 met the law’s demands, mostly because it contains something essential to the frog’s breeding habits: “ephemeral ponds.” It is a ­poetic appellation for low areas that fill with water at certain times of the year and then dry out. Such ponds are unable to sustain fish, which would eat the frog’s eggs.

Poitevent notes the specific requirements of what he points out used to be called the Mississippi gopher frog. “They’re very delicate creatures, aren’t they?” he asks. “They look so prehistoric, and yet, they are quite delicate.”

Jaime Smith, the most recent in a long line of researchers who have come to Mississippi to help restore the frog population, says: Not really. The frog got along fine until people came along.

“The main driver of its near extinction was human activity and habitat loss, fragmentation and degradation,” she said last month as she led a visitor on a search for the frog.

“So when I hear the argument that this is an animal that clearly wasn’t meant to survive anyway, I feel it’s kind of like if someone broke into your apartment, trashed it and said you weren’t really meant to have this apartment anyway.”

Others may listen to the dusky gopher frog and detect a snore. Smith hears more of a purr.

“They’re great little animals,” she said.

Smith, 27, has been known to bolt from gatherings on evenings during breeding season, when the water levels in the ephemeral ponds have reached at least 55 centimeters and the rain is falling.

In the middle of the night, she briefly detains frogs headed to the pond for a quick examination, then sends them on their way. Later, she will collect some of their egg masses to raise in captivity. There was a setback a couple of years ago: A protozoan parasite decimated her efforts. She collected 121 egg masses — each with about 1,200 eggs — and only two tadpoles metamorphosed.

On a recent excursion into the national forest, a reporter and photographer were asked to disable the GPS on their devices to keep the frogs’ whereabouts a secret. The dusky gopher frog spends most of its time underground, living in tree stumps and holes created by gopher tortoises, hence its name.

In one part of the forest, researchers are testing whether the frogs would be just as happy in a hole in the ground drilled by a two-inch auger. Smith pulled out a mesh liner, and there indeed was one of the endangered amphibians.

When protection efforts began, there were only about 100 frogs capable of reproduction. That number has doubled, Smith said. And she acknowledges it takes a lot of work to keep the frog happy.

Besides the rare ponds, the frogs require an “open canopy” forest that lets in plenty of sunshine, and their protected areas are regularly burned to kill off the undergrowth that would make it hard for the frogs to commute to the ponds.

Therein lies the rub, according to Poitevent and Weyerhaeuser. Unit 1 has the ephemeral ponds, but none of the other characteristics the frog needs, they contend. Putting additional conditions on their land could keep it from being developed, and devalue the property by as much as $33 million over the next 20 years.

If that happens in a rural part of Louisiana, they argue, it could happen anywhere. “Vast portions of the United States could be designated as critical habitat if a single feature used by an endangered species is present,” the company argues in its brief.

The government downplays that, saying the designation causes no immediate problem for the landowners. It might be needed only if things go south for the frog in Mississippi, and the land could be made habitable for the frog with reasonable effort, “distinguishing it from other historically occupied sites where such restoration is not readily feasible.”

So far, courts have found the government’s efforts a reasonable interpretation of the Endangered Species Act. And the Trump administration is defending the designation of the land, even as it proposes changes in the act that environmentalists complain would weaken it.

Poitevent is among those surprised by the Trump administration’s support of the frog.

“I thought that was curious, yes,” he said. “I had hoped they would change (sides), and they are not.”